The purpose of the study is to report an unusual case of encapsulated iron intraocular foreign body (IOFB) of long duration presenting with cystoid macular edema (CME) and normal full-field electroretinogram (ERG). A 28-year-old male presented with a history of metal injury 5 years back and subsequent visual loss in the left eye for 3 months. Fundus examination of the left eye showed an encapsulated cyst-like structure inferior to the disc with the surrounding pigmentary changes and CME. B-scan ultrasonography and computed tomography scan confirmed metallic IOFB. A full-field ERG performed before surgery showed a normal response. He underwent pars plana vitrectomy with IOFB extraction and silicone oil injection as a tamponade. Two months later, silicone oil removal was combined with intravitreal triamcinolone acetonide (IVTA) injection for persistent edema. Meticulous clinical evaluation, imaging, electrophysiological testing coupled with surgical intervention, and IVTA injection resulted in resolution of CME with minimal visual improvement. In conclusion long-standing encapsulated iron IOFB on the retina can cause vision-threatening complications without siderosis.

We report an interesting, and to our best knowledge, previously unreported association of an encapsulated iron IOFB of long duration presenting with cystoid macular edema (CME) and normal full-field ERG.

Case Report

A 28-year-old male presented to us with gradual progressive visual loss in the left eye for 3 months. He gave a history of injury to the left eye 5 years back while hammering a metal piece. His best-corrected visual acuity was 20/20 OD and 20/200 OS. Anterior segment examination of the left eye revealed nebulomacular corneal scar, quiet anterior chamber, and clear lens. Fundus examination of the left eye showed engorged retinal vessels with CME. An encapsulated cyst-like structure of two-disc diameter size inferior to the disc was noted with the surrounding pigmentary changes [Figure 1]a. Ocular coherence tomography (OCT) showed CME with subretinal fluid (SRF) in the left eye [Figure 2]a. B-scan ultrasonography confirmed metallic IOFB. Computed tomography of the left orbit showed a hyperdense structure impinging on the posterior surface of the left globe [Figure 3]. A full-field ERG performed before surgery showed normal response.

Pars plana vitrectomy (PPV) with IOFB extraction was contemplated. Considering the large size of the IOFB, it was planned to remove IOFB through the limbal route after clear lens extraction.

A 6-mm triplanar sclerocorneal tunnel was made before the vitreoretinal procedure. The tunnel was made 2 mm from the limbus in the superior quadrant. Nucleus was removed through the tunnel, using irrigation and aspiration mode of the phacoemulsification machine.

Care was taken to create good anterior continuous circular capsulorhexis. Sclerocorneal incision was temporarily closed with a single 10.0 nylon suture.

This was followed by standard three-port PPV. A 23-gauge infusion port and handheld light source were combined with 20-gauge vitrectomy port. Core vitrectomy was combined with 360° scleral indentation and removal of vitreous debris. The metallic IOFB [Figure 4] measuring 3 mm in size was found embedded in the retina inferior to the disc. Vitreoretinal adhesions around the IOFB were released with the help of vitreous cutter. Vitrectomy cutter was used to make a smooth posterior capsular opening. A 20-gauge diamond-coated IOFB forceps was introduced through the vitrectomy port.

The IOFB along with the capsule was lifted through the posterior capsule opening to the iris plane and removed through the sclerocorneal tunnel with McPherson forceps. The retinal defect was surrounded by endolaser. After removal of IOFB, three-piece polymethylmethacrylate intraocular lens was placed in the sulcus over the anterior capsular rim. Silicone oil was used as endotamponade. Ports were sutured.

Cases diagnosed with retained metallic IOFBs, seen shortly after trauma, have been advised removal to prevent retinal toxicity.

However, long-standing and encapsulated IOFBs embedded in the retina have conventionally been observed.[3]

This is mainly because encapsulated IOFB has remained for long periods in the posterior segment without any ERG changes, ocular complications or inflammatory response.[3],[4]

Moreover, delayed IOFB removal is associated with difficulty in removing the thick and dense scar tissue efficiently with IOFB still embedded in the remaining dense tissue.[5]

Peyman et al. performed lensectomy-vitrectomy in three eyes with long-standing encapsulated and firmly embedded IOFB.[3] However, IOFBs were not removed, as it was assumed that aggressive removal could cause trauma to the retina. In these eyes, ERG had remained normal over a period of 47–60 months.

In a study conducted by Neumann et al., out of ten eyes harboring metallic IOFBs for 9 to 46 years, only one patient had reduced ERG that was clearly related to the toxic effect of IOFB.[6]

On the other hand, various studies in the literature have pointed out that an envelope of dense fibrous tissue did not always prevent the spread of metallic ions.[5]

Few cases of encapsulated IOFB with ocular siderotic changes[7] localized siderotic changes in the vicinity of IOFB[4] and ERG changes without siderosis[8] have been documented.

The extent to which degenerative changes becomes evident also varies with the size, chemical composition, or position in the eye.[4],[5]

Our patient had large encapsulated IOFB of 5-year duration with normal ERG. Although there was no pathologic confirmation, we believe encapsulation limited free passage of ferrous ions and siderosis.

The IOFB although encapsulated and outside the macula caused some localized retinal toxicity in the form of CME. We postulate that it could be secondary to subclinical chronic inflammation or limited low dose of ion diffusion through the capsule. Despite normal ERG, the presence of CME prompted its surgical removal. The CME resolved with IVTA injection.

At the last follow-up 13 months post-PPV, CME had resolved with minimal visual improvement.

Hence, we recommend that encapsulated IOFB without siderotic changes and normal ERG can present with subtle clinical signs which should not be overlooked. IOFB in such scenarios needs removal rather than observation.

Conclusion

Long-standing encapsulated iron IOFB on the retina can cause vision-threatening complications without siderosis. Normal ERG in such cases can be misleading for its surgical removal.

We report a rare case of encapsulated IOFB causing a localized retinal toxicity limited to the macula which responded to IOFB removal and adjuvant IVTA treatment with minimal visual improvement.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understand that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.